Integrated fuel cell and fuel conversion apparatus

ABSTRACT

A pair of reaction vessels provide hydrogen to a fuel cell by making hydrogen in one of the vessels while simultaneously regenerating the other vessel, and then reversing the function of the vessels. In the vessel making hydrogen a hydrocarbon feedstock is cracked and steam reformed using sensible heat generated during the regeneration of the vessel. Regeneration includes preheating, separately within the reaction vessel, fuel cell fuel electrode exhaust and an oxygen containing gas. Preheating is accomplished using the heat of combustion and/or sensible heat stored within material disposed within the vessel while it is making hydrogen. After being preheated the fuel electrode exhaust and oxygen containing gas are allowed to mix and combust within the vessel, thereby heating materials disposed therein. This heat is the heat used to crack and steam reform the hydrocarbon fuel.

RELATED APPLICATION

U.S. patent application Ser. No. 21,393 titled "Reaction Apparatus forProducing A Hydrogen Containing Gas" by Richard A. Sederquist, filed oneven date herewith and of common assignee with the present application,describes and claims subject matter which is related to the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and apparatus for producing a hydrogencontaining gas from a hydrocarbon feedstock.

2. Description of the Prior Art

In the prior art, producing a hydrogen containing gas, such as hydrogen,from a hydrocarbon feedstock is typically accomplished by passing thefeedstock (and steam if the conversion process is steam reforming)through catalyst filled tubes disposed within a furnace. Fuel and airare burned within the furnace to provide heat for the catalytic reactiontaking place within the tubes. In order to improve the efficiency ofsuch apparatus some efforts have been directed to improving theuniformity of heat distribution to the tubes within the furnace whileminimizing the amount of energy used to produce each unit of hydrogencontaining gas. For example, in commonly owned U.S. Pat. No. 4,098,587to R. A. Sederquist et al the reaction tubes are clustered closelytogether in a furnace, with baffles and sleeves surrounding each tube toimprove heat transfer from the combusting gases in the furnace into thecatalyst beds. Each catalyst bed is annular; and a portion of the heatin the product gases leaving the bed is returned to the bed to furtherthe reaction process by flowing these product gases through a narrowannular chamber along the inside wall of the annular catalyst bed. Theexample given in column 7 of the Sederquist et al patent indicates thatan overall reactor thermal efficiency of 90% was achieved with theapparatus described therein. Other commonly owned patents of a somewhatsimilar nature are U.S. Pat. Nos. 4,071,330; 4,098,588; and 4,098,589.

One drawback of the approaches taken in all of the foregoing patents isthat the heat for the conversion process is still provided indirectly bymeans of heat transfer through reactor walls. Also, a considerableamount of heat energy leaves the furnace with the furnace exhaust gases.Although some of this heat can be recovered and used for other purposes,such as producing steam, it would be more beneficial if this heat energycould be used in the conversion process.

Another process and apparatus for the catalytic conversion ofhydrocarbons by steam is shown and described in a paper titled"Conversion Catalytique et Cyclique Des Hydrocarbures Liquides etGazeux" published by Societe Onia-Gegi. That system comprises a firstvessel including a first heat exchange chamber, followed by a secondvessel containing a catalyst bed, followed by a third vessel including asecond heat exchange chamber. In operation, steam is introduced into thefirst vessel and is preheated as it passes through hot checkerbricksdisposed within the chamber. Downstream of the checkerbricks thepreheated steam is mixed with a hydrocarbon feedstock and the mixturepasses into the second vessel containing a heated catalyst bed by meansof a conduit interconnecting the two vessels. Conversion takes place asthe mixture passes through the heated catalyst bed. Hot conversionproducts leave the second vessel and enter the third vessel, whereuponthe hot conversion products give up heat to checkerbricks which aredisposed therein. The conversion products may then be stored or useddirectly.

When the temperatures in the first heat exchange chamber and in thecatalyst bed are too low to convert the feedstock, the apparatus isswitched to a regeneration cycle. In the regeneration cycle air isintroduced into the third vessel and is preheated as it passes throughthe checkerbricks disposed therein which were heated during theconversion cycle. Downstream of the checkerbricks a fuel, such as oil,is mixed with the preheated air and combusts. In order to keepcombustion temperatures within acceptable limits, air in excess of thatrequired for stoichiometric combustion is used. The hot combustionproducts are directed into the second vessel and pass through thecatalyst bed, therein heating the same. This is the heat which is usedduring the conversion cycle. Because of the excess air, the catalyst bedis oxidized, although this is not desirable. (During the conversion modeof the cycle the oxidized catalyst is reduced back to the metal; thisrequires use of some of the hydrogen being manufactured, and has anegative impact on efficiency).

After passing through the catalyst bed the combustion products aredirected into the first vessel and give up additional heat to thecheckerbricks disposed therein. This is the heat which is used topreheat the steam during the conversion cycle.

Commonly owned U.S. Pat. No. 3,531,263 describes an integrated reformerunit comprised of a can-type structure which houses the reactioncomponents of a system for converting hydrocarbon feedstocks tohydrogen. This compact apparatus, in one embodiment, comprises a centertube containing a volume of reform catalyst, followed immediately by aregion of heat transfer packing material, followed by a volume of shiftconversion catalyst. Surrounding the tube over its entire length is anannular passage. Air is introduced into the end of the annular passageadjacent the shift catalyst volume of the center tube. It is mixed withfuel approximately adjacent the interface between the heat transferpacking material and the reform catalyst. The fuel and air burn andtravel further downstream around the outside of that portion of thecenter tube carrying the reform catalyst. Simultaneously a mixture of ahydrocarbon feedstock and water enter the center tube at the reformcatalyst end. Steam reforming takes place within the catalyst bed withthe heat being provided by the hot combustion products flowingcountercurrent in the annulus around the outside of the tube. As thereform products leave the catalyst bed they give up heat to the heattransfer packing material in the next following region. This heat isused to preheat the air flowing around the outside of this heat transferregion before the air is mixed with the fuel and burned. The cooledproducts from the packing material region then pass through the shiftconversion catalyst volume whereupon carbon monoxide present therein isconverted to additional hydrogen and carbon dioxide. This reaction isexothermic, and the heat produced thereby preheats the air flowingaround the outside of the tube.

While the foregoing apparatus is compact, and careful attention has beengiven to the overall heat balance and heat requirements of the hydrogengenerating reaction, most heat transfer is still indirect and asignificant amount of the heat energy generated within the apparatus,leaves the apparatus with the combustion exhaust and the reformproducts.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a novel, highlyefficient method and apparatus for converting a hydrocarbon feedstockinto a hydrogen containing gas.

A further object of the present invention is compact apparatus for theconversion of a hydrocarbon feedstock to a hydrogen containing gas.

Yet another object of the present invention is a method and means forefficiently integrating a fuel cell with apparatus for converting ahydrocarbon feedstock to hydrogen.

According to the present invention a continuous supply of hydrogen isprovided to a fuel cell from a pair of reaction vessels by makinghydrogen in one of the vessels while simultaneously regenerating theother vessel, and then reversing the function of the vessels. In thestep of making hydrogen, a hydrocarbon feedstock and steam flows intothe vessel and is cracked and steam reformed using sensible heat whichwas generated therein during the regeneration of the vessel; and thestep of regenerating the vessel includes directing the fuel cell fuelelectrode exhaust and an oxygen containing gas into the vessel,preheating the fuel electrode exhaust and oxygen containing gasseparately within the vessel, and mixing these preheated gases andcombusting them within the vessel, wherein the step of preheating isaccomplished using the heat of combustion and/or sensible heat storedwithin material disposed within the vessel during the making of hydrogentherein.

In a preferred arrangement, the oxygen containing gas used duringregeneration is the exhaust from the cathode electrode of the fuel cell.Since both the anode and cathode exhausts contain water vapor which isproduced by the fuel cell, the exhaust from the reaction vessel beingregenerated will also contain steam. A portion of the exhaust from thisreaction vessel may, therefore, be utilized as the steam supply in thereaction vessel which is making hydrogen. This eliminates the need for aseparate steam source, such as a boiler and improves the overall systemefficiency.

Hereinafter, for the purposes of a more general discussion of thedetailed operation of the reaction vessels per se, the fuel electrodeexhaust is referred to as a "hydrogen purge gas", since the reactionvessels, per se, can be regenerated using any gas containing as leastsome hydrogen. The purpose of the hydrogen purge gas is simply tocombust with the oxidant (e.g. air) which is also introduced into thevessel during regeneration. The hydrogen purge gas may also containother combustibles, such as carbon monoxide and methane. Heavierhydrocarbons are undesirable (but not necessarily intolerable) sincethey could form carbon upon cracking. The purge gas may also includenoncombustibles, such as carbon dioxide, water vapor and nitrogen. Inaddition to fuel cell anode exhaust, hydrogen purge gas may be, forexample, pure hydrogen or the purge effluent from well known pressureswing adsorption type hydrogen purification systems.

Preferably each reaction vessel has three zones arranged in sequence.During the making of the hydrogen (i.e., make mode) the hydrocarbonfeedstock and steam are preheated within the first zone which is filledwith material which was heated during regeneration of the reactionvessel. Gasification (i.e., cracking and reforming), of the feedstockand steam mixture takes place within the next following second zone ofheated material which includes a region of reform catalyst. The gas soproduced is then cooled in a lower temperature third zone, therebyincreasing the temperature of the material within the third zone. Theheat used in making the hydrogen is restored by regenerating thereaction vessel (i.e., regeneration mode). Regenerating is accomplishedby separately preheating, within the vessel, a hydrogen purge gas (suchas the fuel cell anode electrode exhaust) and an oxygen containing gas(such as air) using the sensible heat stored during the make mode inmaterial disposed in the vessel. The preheated hydrogen purge gas andair are then permitted to mix together and burn within the second of theabove-mentioned zones to reheat the material in that zone. Combustionproducts from the second zone are then cooled by passing them throughthe first zone, whereby material in the first zone is reheated.

The reaction vessels of the present invention are very compact andhighly efficient. All of the energy expended in the method is utilizedto directly convert the feedstock to hydrogen. Virtually all heattransfer is direct, which eliminates losses typically associated withindirect heating and cooling. Preheating of both the hydrogen purge gasand the oxygen containing gas without using an external heat source alsoincreases efficiency by recovering the maximum amount of heat from theproduct gas of the make mode. Maximizing preheating minimizes the amountof hydrogen purge gas which must be burned to provide process heat,which also increases efficiency. Thermal efficiencies of 97% and perhapshigher can be obtained by the method of the present invention.

Separate preheating of the hydrogen purge gas and oxygen containing gasduring regeneration is also an important aspect of the presentinvention. In one embodiment this may be done by preheating the oxygencontaining gas within separate conduits disposed within the reactionvessel. This allows both gases to be preheated simultaneously with nocombustion occurring until the oxidant exits the conduits. If thecombustion products are assumed to travel in a downstream direction,reform catalyst may be disposed in the reaction vessel upstream of theoxidant conduit outlets without fear of catalyst oxidation. Separatepreheating within the reaction vessel of the hydrogen purge gas and theoxygen containing gas provides other advantages which will be explainedin more detail in the Description of Preferred Embodiments.

The foregoing and other objects, features, and advantages of the presentinvention will become more apparent in the light of the followingdetailed description of preferred embodiments thereof as illustrated inthe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front view, partly broken away, of a pair of catalyticreaction vessels according to the present invention.

FIG. 2 is a front view, partly broken away, of another catalyticreaction vessel according to the present invention.

FIG. 3 is a graph of simplified temperature profiles within thecatalytic reaction vessels of FIG. 1.

FIG. 4 is a vertical, cross-sectional view of yet another catalyticreaction vessel according to the present invention.

FIG. 4A is a graph showing actual temperature profiles within thereaction vessel of FIG. 4.

FIGS. 5A, 5B, 6A, 6B and 7 are schematic diagrams of systems whichinclude catalytic reaction vessels integrated with fuel cells inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As an exemplary embodiment of the present invention consider the pair ofreactors 10 and 10A shown in FIG. 1, which are designed to producehydrogen. These reactors are identical. Corresponding elements of thetwo reactors are given the same reference numerals, except that thenumerals are followed by the letter A for elements of the right-handreactor. The reactors 10 and 10A operate in conjunction with each other,such that while one is in the "make mode" (i.e., making hydrogen) theother is in the "regeneration mode" (i.e., being regenerated). After asuitable period of time the reactors switch modes. Thus, at any point intime, one of the reactors is making hydrogen while the other reactor isbeing regenerated. Of course, if a continuous flow of hydrogen gas isnot required, then only a single reactor could be used. Hereinafter theoutput from the reactor in the make mode is sometimes referred to as the"product gas". For the purposes of explanation, the reactor 10, on theleft, is considered to be in the make mode, and the reactor 10A on theright is in the regeneration mode.

The reactor 10 is here shown as comprising a cylindrical reaction vessel12. At the bottom end of the vessel is a steam and hydrocarbon feedstockinlet 14 and a combustion products outlet 16. At the top end of thevessel is a product gas outlet 18, an oxygen containing gas inlet 20 ,and a hydrogen purge gas inlet 22. In this embodiment the oxygencontaining gas is air. Disposed within the vessel 12 are a plurality ofcylindrical conduits 24 having inlets 26 and outlets 28. The inlets 26are in gas communication with the air inlet 20. Flow into inlets 14, 20,and 22 is controlled by valves 30, 32, and 34, respectively. Flow fromthe outlets 16 and 18 is controlled by valves 36 and 38, respectively.As shown in the drawing, during the make mode, the valves 30 and 38 areopen while the valves 32, 34, and 36 are closed.

From an operational point of view, the vessel 12 may be thought of ascomprising three zones arranged in sequence or series gas flowrelationship within the vessel. The zones are labeled zone 1, zone 2,and zone 3 in the drawing. Imaginary lines L₁ and L₂ have been drawn infor the purpose of visualizing and discussing where one zone ends andthe next begins, although in actual operation the point where one zoneends and the next begins cannot be so precisely defined.

During the make cycle a mixture of steam and hydrocarbon feedstockenters zone 1 of the reaction vessel 12 via the inlet 14. Zone 1 isfilled with an inert packing material 39, such as alumina, which hasheat stored therein from the regeneration cycle. The mixture of steamand feedstock entering zone 1 are at a lower temperature than thetemperature of the packing material, and thus heat is transferred to themixture from the packing material as the mixture passes through zone 1.The hydrocarbon feedstock may be either in the form of a gas, such asnatural gas, or in the form of a vaporized liquid hydrocarbon, such asnaptha, No. 2 heating oil, or the like.

The end of zone 1 is considered to be that location within the vessel 12wherein the steam and feedstock mixture have been heated to atemperature high enough such that cracking and/or reforming of thefeedstock begins to occur. At this point the mixture is considered to beentering zone 2. Thus, zone 1 may be thought of as a preheating zoneduring the make mode. Within zone 2, cracking and reforming of thefeedstock takes place. The temperature at the inlet of zone 2 willprobably be somewhere between 700° F. and 1000° F., depending upon thefeedstock being used and the matieral within the reactor (i.e., inert orcatalytic). In this embodiment, zone 2 is divided into two regionslabeled region 1 and region 2. Disposed within region 1 is anonreducible and nonoxidizable (i.e., inert) packing material; and inregion 2, which is immediately downstream of and in series gas flowrelationship to region 1, is reform catalyst 42 which surrounds thelower end portions 44 of the conduits 24. The reform catalyst willtypically be a metal supported on an inert ceramic material. Forexample, a common reform catalyst is nickel supported on alumina. Thepacking material 40 in region 1 may be, for example, alumina, ormagnesium oxide pellets, and may be the same as the material 39 inzone 1. The packing material 40 will be, on average, considerably hotterthan the material in zone 1 as a result of combustion taking placetherein during the regeneration mode. As the effluent from zone 1travels through region 1 of zone 2, the heat needed for gasification isprovided by the sensible heat in the packing material 40. Thetemperature of the effluent from region 1 is sufficiently high toprovide the heat required for the additional reforming of thehydrocarbon feedstock (within region 2) without adding heat fromexternal sources.

The end of zone 2, which is the beginning of zone 3, is considered to bethe location within the reaction vessel 12 wherein no furthersubstantial gasification takes place. Zone 3, in this embodiment,contains only inert packing material, and is a cooling zone during themake mode. As the effluent from zone 2 is cooled, it transfers heat toinert packing material disposed in zone 3 around the conduits 24. Inthis embodiment the conduits 24 are empty, but they, too, could befilled with inert packing material, which would be heated indirectly bythe zone 2 effluent. The length and volume of zone 3 is preferablyselected so as to cool the effluent from zone 2 to a preselectedtemperature. The cooled effluent is then exhausted from the reactionvessel 12 via the outlet 18. This effluent is the reactor product gas.In addition to hydrogen it contains carbon monoxide, carbon dioxide,methane, and water.

Although not the case in this embodiment, zone 3 may include a region ofshift catalyst in place of a portion of the inert packing material.Within the shift catalyst region carbon monoxide and water in theeffluent from zone 2 would combine to produce additional hydrogen andcarbon dioxide in a manner well known to those skilled in the art. Thisis very desirable when the product gas made in the reactor 10 is to beused in a phosphoric acid electrolyte fuel cell which cannot toleratemore than a few percent of carbon monoxide. If desired the carbondioxide could be removed downstream of the reactor using well knownscrubbing devices; but this is not necessary if the product gas is to beused in a phosphoric and electrolyte fuel cell.

Turning now to the regeneration cycle, which is occurring in reactor10A, the valves 30A and 38A are closed and the valves 32A, 34A, and 36Aare open. Air enters the vessel 12 and conduits 24 via the inlet 20. Ahydrogen purge gas, as hereinbefore defined, enters the reaction vessel12A via the inlet 22A and travels through the inert packing material 46Ain zone 3 picking up heat therefrom. The air is kept separate from thehydrogen purge gas in zone 3 so that no combustion occurs within zone 3during regeneration. Air also picks up sensible heat from thesurrounding packing material. The packing material 46A is thereby cooledsomewhat during the regeneration cycle. It is, of course, reheatedduring the make cycle when it performs the function of cooling theproduct gases.

The air is exhausted from the outlets 28A of the conduits 24A into thepacking material 40A of zone 2, whereupon it mixes with the hydrogenpurge gas from zone 3 which has just passed through the reform catalystin region 2. By this time, the hydrogen purge gas and air have beenpreheated to a temperature sufficiently high to result in essentiallycomplete combustion of the hydrogen purge gas within the reactionvessel. As combustion occurs, and as the combustion products travelthrough zone 2 and zone 1 and are eventually exhausted via the outlets16A, heat is transferred to and stored in the packing material 40A and39A. It is this stored sensible heat within the reaction vessel which isused to preheat, crack and reform the hydrocarbon feedstock during thereactor's make mode of operation. Preferably, combustion of the hydrogenpurge gas is completed within zone 2, and zone 1 simply serves thepurpose of cooling the products of combustion to a desired temperature.

The advantages of the present invention are many. One of the majoradvantages is the extremely high reactor thermal efficiency. In a systemdesigned simply to produce hydrogen, the reactor thermal efficiency isgiven by the following equation: ##EQU1## where A is the total amount ofhydrogen produced by the reactor;

B is the total amount of hydrogen in the purge gas which is burnedduring regeneration;

C is the total amount of hydrocarbon feedstock fed to the reactor;

LHV_(H).sbsb.2 is the lower heating value of hydrogen, and

LHV_(f) is the lower heating value of the hydrocarbon feedstock.

Note that (A-B) is equivalent to the net amount of hydrogen produced bythe reactor. When maximum efficiency is achieved, the temperature of thepacking material 39 at the inlet to zone 1, at the completion of themake mode of operation, should be very close to its temperature at thecompletion of the regeneration mode. Further, the temperature of thepacking material 46, at the exit of zone 3 at the completion of the makemode, should be very close to its temperature at the completion of theregeneration mode.

Another important advantage of the foregoing embodiment of the presentinvention is that an excess of oxygen can be passed through the reactionvessel to ensure complete combustion of the hydrogen purge gas withoutany combustion taking place within the reform catalyst contained in thereaction vessel. This is accomplished by the conduits 24, which preventmixing of the hydrogen purge gas and air until both are downstream ofthe reform catalyst. In another embodiment, hereinafter to be described,the same advantage is obtained even though the hydrogen purge gas andair are permitted to mix and burn upstream of a reform catalyst region.

Although in this exemplary embodiment region 1 contains no reformcatalyst, it may be desirable to include some reform catalyst in thisregion to enhance steam reforming during the make mode. If this is doneit is preferable to minimize or not to use any excess air duringregeneration in order to limit the occurrence of catalyst oxidation andthe subsequent reduction of the catalyst which would take place duringthe make mode.

It is possible to utilize the method of the present invention with noregion of reform catalyst. In other words, zone 2 may be filled withonly nonreducible, nonoxidizable packing material. Conversion of thehydrocarbon feedstock to hydrogen or to other low molecular weighthydrocarbons will not, however, be as complete as when a reform catalystregion is also used; however, conversion may be adequate for certainapplications.

An alternate embodiment of the present invention is described withreference to FIG. 2. The reactor 50 of FIG. 2 differs from the reactors10 and 10A of FIG. 1 only in the location of conduits 52 which carry theair or other oxygen containing gas into zone 2. Rather than beingdisposed within zone 3, as in the previous embodiment, in thisembodiment they lie within zones 1 and 2. During regeneration, the airenters the reactor 50 by an inlet 54 at the bottom of the reactionvessel 55, and from there travels into the inlet ends 56 of the conduits52. The air exits the conduits 52 at their outlet ends 58 which are atsubstantially the same location as the outlet ends 28, 28A of thereactors 10, 10A. Hydrogen purge gas enters the reaction vessel at theinlet 60, is preheated in zone 3, and mixes with the air from theconduits 52 at about the interface between regions 1 and 2 in zone 2, asin the foregoing embodiment. Combustion of the air and hydrogen purgegas occurs within zone 2, and cooling of the combustion products occursin zone 1, as was also the case in the foregoing embodiment. In thisembodiment, however, the air is preheated by heat from the combustion ofthe gases which is simultaneously occurring around the outside of theconduits 52. The combustion products leave the vessel 55 via the outlet62. In the make mode feedstock and steam enter the vessel 55 via theinlet 64; and reaction products (i.e., the hydrogen containing gas)leave the vessel via the outlet 66.

FIG. 3 is a graph which, in a simplified manner, depicts the temperatureswings which occur within the reaction vessel of FIG. 1 over a period oftime. Temperature is represented on the horizontal axis; and thelocation within the reaction vessel is represented by the vertical axis.For simplicity, the vertical axis is only divided up into zones 1, 2 and3, with zone 2 being broken down into regions 1 and 2. The curve Arepresents the temperatures which exist within the reaction vessel atthe very end of the make cycle or make mode of operation. The curve Brepresents the temperatures attained within the reaction vessel at thevery end of the regeneration cycle. Note from curve B that immediatelyafter regeneration the temperatures in zone 3 are lowest, since the heatstored therein during the make cycle has been used to preheat thehydrogen purge gas and oxygen containing gas. The highest temperaturesexist in region 1 of zone 2, within which combustion is initiated andtakes place. The temperature falls off thru zone 1 since the combustionproducts transfer heat to the packing material in zone 1. During themake cycle the temperatures represented by the curve B move toward thetemperatures represented by the curve A, which are the temperatures atthe end of the make cycle. Thus the temperatures drop within zone 1 andmost of zone 2 since the preheating of the steam and feedstock as wellas the gasification of the feedstock utilize the sensible heat stored inthese zones. In zone 3, and region 2 of zone 2, the temperatureincreases as the hotter effluent from region 1 passes therethrough andis cooled as it transfers heat thereto. In operation, when thetemperatures depicted by curve A are reached, the making cycle stops andregeneration begins. Ideally the curves A and B meet at the beginning ofzone 1 and at the end of zone 3. Actual data (which is hereinafterpresented with regard to yet another embodiment of the presentinvention) shows that it is possible to come quite close to this idealsituation. This data will also show that the temperature swings whichoccur during the practice of the present invention are quite small,which minimizes thermal shock and stresses to and within the reactionvessel.

FIG. 4 shows an embodiment of the present invention which incorporateswhat is herein called staged combustion. in FIG. 4 only a single reactor100 is shown, although for the continuous production of hydrogen a pairof reactors 100 would be used in the manner discussed with respect tothe embodiment of FIG. 1. The reactor 100 includes a cylindricalreaction vessel 102. The vessel 102 comprises: a steam inlet 101,including a valve 103; a feedstock inlet 104, including a valve 105; acombustion product outlet 106, including a valve 107; an air inlet 108,including a valve 109; a hydrogen purge gas inlet 110, including a valve111; and a product gas outlet 112, including a valve 113. Disposedwithin the vessel 102 is a single air tube 114 having outlets 116, 118,and 120 along its length. In actual practice, the number of air tubesused would depend upon the size of the reaction vessel.

Once again, in accordance with the present invention, the reactionvessel 102 comprises three zones arranged in series gas flowrelationship within the vessel. These zones are labeled 1, 2 and 3 inthe drawing. Beginning at the bottom of the vessel, zone 1 includes aregion 122 of inert heat transfer packing material followed by a plenumregion 124. Zone 2 begins with a region 126 of inert heat transferpacking material. This region is followed by a region 128 filled with amixture of two parts inert heat transfer packing material to one partreform catalyst, respectively. Next are inert packing region 130, reformcatalyst region 132, inert packing region 134, and reform catalystregion 136. Zone 3 begins with a region 138 of inert heat transferpacking material, followed by a region 140 of high temperature shiftcatalyst, followed by a region 142 of low temperature shift catalyst.The three air tube outlets 116, 118 and 120 are located, respectively,at the interface between regions 134 and 136, at the interface betweenregions 130 and 132, and at the interface between regions 126 and 128.

In operation, during the hydrogen making mode the valves 103, 105 and113 are open and the valves 107, 109 and 111 are closed. Steam entersthe inlet 101 and is preheated in region 122 of zone 1. A liquidhydrocarbon feedstock is introduced into the plenum region 124 via theinlet 104 wherein it vaporizes and mixes with the preheated steam fromthe region 122. The plenum region 124 includes an open volume 125 whichensures good vaporization and mixing. Of course, as in the embodiment ofFIG. 1, the hydrocarbon feedstock could be premixed with the steamupstream of the inlet 101 whereupon a plenum region within the vessel102 would not be used.

Upon exiting the plenum region 124, or very shortly thereafter, themixture of hydrocarbon fuel and steam will have reached a temperaturehigh enough to result in the initiation of gasification (i.e., crackingand reforming) of the hydrocarbon fuel. Cracking and reforming continuesthrough zone 2, the heat for the reactions being the sensible heat whichwas stored within the materials in zone 2 during the regenerating modeof the cycle, hereinafter described.

The effluent from zone 2 then passes through the somewhat lowertemperature region 138 of inert packing material, transferring heatthereto. The effluent continues through the high temperature shiftcatalyst region 140 and the low temperature shift catalyst region 142.In the high temperature shift catalyst region 140 and the lowtemperature shift catalyst region 142 carbon monoxide reacts with waterto form carbon dioxide and hydrogen, and heat is released which isstored in the shift catalyst regions. The effluent from the lowtemperature shift region is the desired product gas of the presentinvention. This gas, which is high quality hydrogen, is exhausted fromthe reaction vessel via the outlet 112.

The reactor is switched to the regeneration mode at any time before thetemperatures therein become too low to efficiently crack and reform thefeedstock. During the regeneration cycle the valves 103, 105, and 113are closed, while the valves 107, 109, and 111 are open. Hydrogen purgegas enters the inlet 110 and is preheated by the sensible heat stored inthe low temperature and high temperature shift catalyst regions 142,140, respectively, and in the inert packing region and the reformcatalyst region 138, 136, respectively. Of course, as the hydrogen purgegas travels through zone 3 and picks up heat therefrom, the temperatureof the materials in zone 3 is somewhat reduced.

Air (or other oxygen containing gas) enters the air tube 114 via theinlet 108 and is also preheated as it travels through zone 3 by the heatstored in the materials which surround the air tube. A predeterminedportion of the air exits the tube 114 at the outlet 116 and mixes withthe hydrogen purge gas at this point, which is just downstream of thereform catalyst region 136. Burning is initiated at this point withinthe vessel 102. Note that, even though both shift catalyst regions 142,140 and the reform catalyst region 136 are used to preheat the air forthe regeneration cycle, none of the air passes through the catalystmaterials within these regions, and the catalysts are thereby protectedfrom oxidation. Since the air, or rather the oxygen in the air, wouldoxidize reform catalyst in regions further downstream of the outlet 116,the quantity of air discharged from the air tube 114 at the outlet 116is predetermined so that it will be substantially completely burnedwithin the immediately downstream inert packing region 134. This is afirst stage of combustion.

The reform catalyst region 132 receives the combustion products from thefirst stage of combustion and the remaining unburned hydrogen purge gas.No substantial amount of oxygen enters this region; however, some of theheat from the combustion products is released to and stored within thereform catalyst. Air from the outlet 118 of the tube 114 is then mixedwith the hydrogen purge gas in the effluent from the region 132. Onceagain, no more air is discharged from the outlet 118 than can besubstantially completely burned within the following inert packingregion 130. This constitutes a second stage of combustion. Some of theheat generated by this combustion is transferred to both the inertpacking material within the region 130 and the reform catalyst/inertpacking mixture within the following region 128. At the end of theregion 128 the remaining air within the tube 114 exits into the inertpacking region 126 from the outlet 120, and mixes with the remainingunburned hydrogen purge gas. This mixture burns within the region 126and transfers heat to the material therein. This is a third and finalstage of combustion. Preferably complete combustion of all thecombustibles in the hydrogen purge gas has taken place within zone 2.The combustion products from zone 2 are then cooled somewhat bytransferring heat to the inert packing material within zone 1, and areexhausted from the raction vessel 102 via the outlet 106.

There are several advantages to using two or more combustion stages ascompared to the single stage combustion of the first describedembodiments. First, with staged combustion it is possible to maintain agreater total volume of reform catalyst at an efficient reformingtemperature, without oxidation of the reform catalyst occurring duringregeneration. Reform catalyst is more efficient at convertinghydrocarbons to hydrogen than simply hot inert packing regions.

A second advantage of staged combustion is a more uniform temperatureprofile through zone 2. With a single stage of combustion duringregeneration all of the oxygen is mixed with the hydrogen purge gas at asingle location. The highest temperatures are generated at this loation,and this temperature tapers off as the combustibles and combustionproducts travel downstream toward the exit. Therefore, when the singlecombustion stage reactor is making hydrogen, the hydrocarbon fuel (i.e.,feedstock) and steam mixture sees its lowest temperature initially, whenit has the highest concentration of fuel and requires a maximum ofenergy, and the highest temperature near the end of the conversionprocess when it is diluted in hydrocarbon fuel and thereby requires lessenergy to complete the conversion. With staged combustion thetemperature profile is maintained more constant since there are separatecombustion regions between regions of reform catalyst. Reforming,therefore, is more efficient.

A subscale reactor identical to the reactor shown in FIG. 4 was builtand tested. The reaction vessel 102 was about six feet long, as shown onthe scale in FIG. 4A, and four inches in diameter. The air tube 114 wastwo inches in diameter. The inert packing material in regions 122, 126,128, 130, 134, and 138 was alumina. The reform catalyst in regions 128,132 and 136 was nickel on alumina. The high temperature shift catalystin the region 140 was iron-chromia; and the low temperature shiftcatalyst in the region 142 was cobalt molybdenum. The mixture in theregion 128 was two parts inert packing material to one part reformcatalyst, by weight.

In initial tests, during regeneration burning of the hydrogen purge gascould not be initiated for the third combustion stage (i.e., in theregion 126 downstream of the air conduit outlet 120) because thetemperature of the mixture of air and hydrogen purge gas at thislocation was too low. Despite this lack of third stage combustion, theregeneration mode was still able to provide adequately high temperaturesthroughout the reaction vessel to crack and reform all of the feedstock.It was, therefore, decided that the third combustion stage wasunnecessary in this particular test apparatus; and the airflows from theoutlets of the air conduits were thereupon adjusted to obtain completeburning of the hydrogen purge gas within the first two combustionstages.

FIG. 4A is a graph similar to the type shown in FIG. 3, but which isplotted from actual test data using the apparatus of FIG. 4 with thehereinabove mentioned adjusted airflow so as to obtain complete burningof the hydrogen purge gas in the first two stages of combustion.Temperature is plotted on the horizontal axis, and the location alongthe length of the reaction vessel is plotted on the vertical axis interms of inches from the bottom of the vessel. The data presented isfrom the 89th cycle of the apparatus. The graph is aligned with and isscaled to correspond in length to the apparatus which is shown in FIG.4.

In this particular test the regeneration mode and the hydrogen make modewere each about two minutes in duration. In FIG. 4A the solid line isthe temperature profile through the reactor at the end of the two minuteregeneration period (i.e., the beginning of the reform period). Thedashed line is the temperature profile at the end of two minutes ofreforming (i.e., the beginning of the regeneration period).

During the make mode the hydrocarbon feedstock was naptha (atomichydrogen to carbon ratio of 1.89) with 160 parts per million sulfur and20% aromatics. The feedstock flow rate was 1.87 lbs/hr.; and the steamto carbon ratio was maintained at 3.50. The operating pressure was 1.0atmospheres. The composition of the product gas was, on a dry basis, 69%H₂, 22% CO₂, 7% CO and about 2% methane. In a full-scale reactor withlarger shift catalyst beds the CO content could be reduced to even lowerlevels. Also, additional shifting could be accomplished in a separatebed outside of the reactor, if necessary.

The vessel was regenerated using simulated exhaust from the anode sideof a fuel cell as the hydrogen purge gas. This simulated anode exhaustcomprised 0.304 lbs./hr. H₂, 0.334 lbs./hr. CO, 4.8 lbs./hr. CO₂ and 8.3lbs./hr/ H₂ O. The airflow rate during regeneration was 11.3 lbs./hr.with 50% of the air being discharged from the outlet 116 and 50% fromthe outlet 118.

In this subscale test the measured efficiency, in accordance withequation (1) above, was about 70%. Efficiency is typically lower forsubscale tests due to the larger heat losses per unit of flow. From thisdata it is projected, using well known procedures, that a full-scaleunit would have an efficiency of about 97%. This projection assumes thata full-scale unit would handle about 2,000 pounds of fuel per hour,would be about 10.0 feet long, 8.0 feet in diameter including internalinsulation and contain 216 air tubes which are each about 6 feet longand 3 inches in diameter. These air tubes could contain internal packingto improve heat transfer during regeneration.

In another experiment, conducted using the same apparatus, the feedstockwas No. 2 fuel oil with 3300 ppm sulfur, by weight, and 28% aromatics.An efficiency of about 70% was measured at a fuel flow rate of 2.0pounds per hour.

As hereinabove discussed, the fuel processing apparatus of the presentinvention can provide the fuel for a fuel cell or for a stack of fuelcells. One possible fuel cell system is shown schematically in FIGS. 5Aand 5B. Fuel reactors, such as those just described are designated bythe numerals 200 and 202. A fuel cell 204 is shown schematically ashaving an anode or fuel electrode 206 and a cathode or oxygen electrode208 separated by an electrolyte soaked matrix 210. In this embodimentthe electrolyte is assumed to be concentrated (96%) phosphoric acid; butfuel cells utilizing other electrolytes could also be used.

Referring to FIG. 5A, in operation a hydrocarbon feedstock and steamfrom any suitable source 212 passes through an open valve 214 and entersthe reactor 200 which is in the make mode. The valve 216 is in a closedposition and prevents the fuel and steam from entering the other reactor202 which is in the regeneration mode. The feedstock and steam areconverted to hydrogen within the reactor 200. The hydrogen leaves thereactor 200 via the conduit 218 and is directed to the anode electrode206 of the fuel cell 204 by way of a valve 220, a hydrogen switchovertank 221, and a conduit 222. The function of the tank 221 will beexplained shortly. Anode exhaust, which contains unconsumed hydrogen,leaves the cell via a conduit 224 and is directed into the reactor 202by way of the valve 220 and a conduit 226. The anode exhaust is thehydrogen purge gas used for regeneration. Air from a suitable source 228passes through an open valve 230 and enters the reactor 202 via aconduit 232. A closed valve 234 prevents air from entering the otherreactor 200. Within the reactor 202 the air from the conduit 232 and theanode exhaust from the conduit 226 combine and burn, in accordance withthe present invention as hereinabove described, and the combustionproducts are exhausted from reactor 202 through an open valve 236. Acorresponding valve 238 associated with the other reactor 200 is closedat this time.

Referring now to FIG. 5B, once the reactor 202 has been regenerated thefunctions of the two reactors are switched by reversing the position ofall the valves. Now the feedstock and steam enter the reactor 202; andthe hydrogen or product gas leaves the reactor 202 via the conduit 226and is directed to the fuel electrode 206 by way of the valve 220, theswitchover tank 221, and the conduit 222. At the same time anode exhaustpasses from the conduit 224 into the conduit 218, and from there intothe reactor 200 along with air from the air supply 228. The combustionproducts from the reactor 200 are exhausted through the now open valve238.

At the instant of switchover the regenerated reactor 202 is filled witha volume of anode exhaust and combustion products which are suddenlydirected toward the anode inlet. The switchover tank, at this moment, isfilled with hydrogen rich product gas. The slug of anode exhaust andcombustion products in the reactor 202 passes through the tank 221 andis thereby diluted with hydrogen rich gas before it enters the fuelcell. This reduces the deleterious effects this slug of gas wouldotherwise have on the cell at each reactor mode change. The switchovertank should have a volume at least several times the void volume of thereactor, which is filled with packing material and catalyst.

FIGS. 6A and 6B depict another fuel cell system in accordance with theteachings of the present invention. This option incorporates andimproves upon the main features of commonly owned U.S. Pat. No.4,128,700 by Richard A. Sederquist, who is also the inventor of thepresent invention. In FIG. 6A the reactor 300 is making hydrogen and thereactor 302 is being regenerated; while in FIG. 6B the reactor 300 isbeing regenerated and the reactor 302 is making hydrogen. As with thereactors 200 and 202 of FIGS. 5A and 5B, the reactors 300, 302 may be ofany configuration which is in accordance with the principles of thepresent invention hereinabove described in connection with FIGS. 1through 4.

Referring first to FIG. 6A, the anode exhaust from a fuel cell 304travels through a conduit 308, a valve 306, and a conduit 310 into thereactor 302. Once again, the anode exhaust is used as the hydrogen purgegas. It contains hydrogen which was not consumed by the fuel cells,water, and other gases. Air enters the cathode compartment of the fuelcell 304 via a conduit 312. The cathode exhaust passes through a valve314 and into the reactor 302 via a conduit 316. The cathode exhaustincludes oxygen from the air which was not consumed by the fuel cell. Italso includes a considerable amount of water which was produced in thefuel cell at the cathode and which is carried away from the fuel cell inthe cathode exhaust. The anode and cathode exhaust mix and burn withinthe reactor 302 in a manner which has already been described in greatdetail. The combustion products, including the water (in the form ofsteam) which was originally in the anode and cathode exhaust, leaves thereactor 302 via a conduit 318; passes through a valve 320 and into aconduit 322. A portion of this exhaust is vented via a conduit 324,while a blower 326, in a conduit 328, pumps a portion of the exhaustthrough the valve 320 and into the reactor 300.

A hydrocarbon feedstock from a source 330 passes through a valve 332 andinto a reactor 300 via a conduit 334. The steam necessary for thereforming reaction is obtained entirely from the recirculated portion ofexhaust from the reactor 302. The reform products from the reactor 300,which in this case comprise essentially hydrogen, carbon dioxide,nitrogen, water vapor, and carbon monoxide, leave the reactor 300 via aconduit 336; pass through the valve 306 and a switchover tank 337; andenter the anode compartment of the fuel cell 304 by way of a conduit338.

In FIG. 6B the function of the reactors 300 and 302 are reversed. Thevalve 306, 314, 320, and 332 are shown in their alternate position. Theanode exhaust is now directed to the reactor 300 via the conduits 308and 336; and the cathode exhaust is directed into the reactor 300 viathe conduits 340 and 342. The combustion products leaves the reactor 300via a conduit 344, and pass through the valve 320 into the conduit 322.A portion of combustion products is vented via the conduit 324, and theblower 326 recirculates the rest to the reactor 302 by way of theconduits 328 and 318. The steam laden exhaust from the reactor 300 mixeswith the feedstock from the supply 330 within the reactor 302, andcracking and steam reforming takes place. The product hydrogen is thendirected to the anode compartment of the fuel cell 304 by way of theconduit 310, switchover tank 337, and conduit 338.

The embodiment just described may be utilized with any acid electrolytetype fuel cell, but is particularly preferred when the fuel cellutilizes concentrated phosphoric acid as the electrolyte.

FIG. 7 shows a system in accordance with the present inventionparticularly suited for use with fuel cells utilizing electrolytes whichare carbonates of alkali metals that are molten at cell operatingtemperatures. Carbonates of potassium, lithium, sodium, and combinationsthereof are most commonly used. Cells using this type of electrolyte aregenerally referred to as molten carbonate electrolyte fuel cells. InFIG. 7 the reactor 400 is making hydrogen while the reactor 402 is beingregenerated. The exhaust from the anode side of a molten carbonateelectrolyte fuel cell 404 is routed through a valve 406 to the reactor402 by way of conduits 408 and 410. The anode exhaust contains hydrogenwhich was not consumed by the fuel cell. It also includes carbon dioxideand water, which are products from the electrochemical reaction whichtakes place in a molten carbonate electrolyte fuel cell.

Air enters the reactor 402 through an open valve 412. The oxygen in theair and the hydrogen and other combustibles in the anode exhaust combineand burn within the reactor 402. The reactor exhaust, which includessteam and noncombustible carbon dioxide, leaves the reactor 402 via aconduit 414; passes through a valve 416; and enters a conduit 418. Aportion of the exhaust is delivered to the cathode of the fuel cell viathe conduits 420 and 422. The carbon dioxide in the exhaust is needed atthe cathode for the fuel cell electrochemical reaction, as is well knownin the molten carbonate fuel cell art. Air, which provides the oxygenfor the electrochemical reaction, is added to the cathode input via aconduit 424.

A blower 428 delivers a second portion of the exhaust from the reactor402 to the reactor 400 by way of a conduit 426, the valve 416, and aconduit 429. This portion of the exhaust includes sufficient water, inthe form of steam, for the steam reforming reaction in the reactor 400.A hydrocarbon feedstock from a source 430 is directed through a valve432 into the reactor 400 by means of a conduit 434. The steam and fuelreact within the reactor 400 in accordance with details of the presentinvention already described, and hydrogen is produced. The hydrogenleaves the reactor 400 via a conduit 436; passes through the valve 406and switchover tank 437; and is directed to the anode of the fuel cellvia the conduit 438.

Once the reactor 402 is regenerated the mode of operation of thereactors is reversed. In this other mode all of the valves are in theiropposite position such that the reactor 400 receives the anode exhaustand air, while the reactor 402 receives the hydrocarbon feedstock and aportion of the exhaust from the reactor 400. The remainder of theexhaust from the reactor 400 is directed to the cathode of the fuel cellvia the conduits 420 and 422. The hydrogen now being produced by thereactor 402 will then pass through conduit 410, the valve 406, theswitchover tank 437, and the conduit 438, and to the anode of the fuelcell 404.

Although the invention has been shown and described with respect to apreferred embodiment thereof, it should be understood by those skilledin the art that other various changes and omissions in the form anddetail thereof may be made therein without departing from the spirit andthe scope of the invention.

Having thus described a typical embodiment of my invention, that which Iclaim as new and desire to secure by Letters Patent of the United Statesis:
 1. In a method for providing a continuous supply of hydrogen fuel toa fuel cell from a pair of reaction vessels, said fuel cell comprising afuel electrode, an oxygen electrode, and an electrolyte disposedtherebetween, the steps of alternately:A. making hydrogen fuel in one ofsaid pair of vessels while simultaneously regenerating the other of saidpair of vessels; and B. regenerating said one of said pair of vesselswhile simultaneously making hydrogen fuel in said other of said pair ofvessels;wherein steps (A) and (B) each comprise the steps of: (a)introducing a hydrocarbon feedstock and steam into a first of saidvessels, which is making hydrogen; (b) cracking and steam reforming saidfeedstock to make said hydrogen in said first vessel using sensible heatstored within said first vessel, said sensible heat being obtained fromthe step of regenerating said first vessel; (c) directing the hydrogenproduced in step (a) to the fuel electrode of the fuel cell; (d)introducing air into the oxygen electrode of the fuel cell; (e)directing the exhaust from the fuel electrode and an oxygen containinggas into the second of said vessels, which is being regenerated; (f)preheating said oxygen containing gas and said fuel electrode exhaustseparately within said second vessel to temperatures high enough toresult in combustion of said oxygen containing gas and said fuelelectrode exhaust if they are mixed together; (g) mixing said preheatedoxygen containing gas and said preheated fuel electrode exhaust withinsaid second vessel and combusting said mixture within said second vesselto regenerate said second vessel by storing within material disposedwithin said second vessel heat from said step of combusting, whereinsaid step (f) of preheating is accomplished using the heat from saidstep of combusting and/or sensible heat stored within said secondvessel; (h) exhausting the products of combustion of step (g) from saidsecond vessel.
 2. The method according to claim 1 wherein the step (a)of introducing steam into said first vessel includes introducing atleast a portion of the exhaust from said second vessel into said firstvessel, said exhaust from said second vessel providing the steam forsaid reforming.
 3. The method according to claim 2 wherein said step (e)of directing an oxygen containing gas into said second vessel includesdirecting exhaust from said oxygen electrode into said second vessel. 4.The method according to claim 2 wherein the electrolyte disposed betweensaid electrodes is molten carbonate and wherein steps (A) and (B) alsocomprise the step of introducing a portion of the exhaust from saidsecond vessel into said oxygen electrode of the fuel cell.
 5. The methodaccording to claim 3 wherein the electrolyte disposed between saidelectrodes is phosphoric acid.
 6. The method according to claim 2including the step of preheating within said first vessel, prior to step(b) of cracking and reforming, one or both of said feedstock and exhaustfrom said second vessel using sensible heat stored within said firstvessel.
 7. The method according to claim 6 wherein the step (b) ofcracking and reforming includes gas flow through said vesselscountercurrent to the direction of flow of the combusting mixture duringstep (g).
 8. A fuel cell system comprising:a fuel cell including a fuelelectrode, an oxygen electrode, and an electrolyte disposedtherebetween; a pair of reaction vessels, each being adapted toalternately make a hydrogen containing gas and to be regenerated, eachof said reaction vessels having an upstream end and a downstream end,each vessel having disposed therein, in sequence from its upstream todownstream end, a first volume of inert packing material containing noreform catalyst, a second volume of material including a first region ofreform catalyst material, and a third volume of material; means foralternately directing a hydrocarbon feedstock and steam first into saidfirst volume of one of said vessels and then into said first volume ofthe other of said vessels; means for directing the hydrogen containinggas produced in the one of said vessels receiving said feedstock andsteam into said fuel electrode of said fuel cell and for directing theexhaust from said fuel electrode into said third volume of material inthe other of said vessels; conduit means within each of said vessels inheat transfer relationship with at least some of said materials disposedin said vessels and including outlet means upstream of said first regionof reform catalyst; means for directing an oxygen containing gas intosaid conduit means, said conduit means constructed and arranged toprevent mixing of the oxygen containing gas and fuel electrode exhaustdownstream of or within said first region of reform catalyst; and eachof said vessels including combustion products outlet means at itsupstream end for exhausting combustion products therefrom duringregeneration of each vessel.
 9. The fuel cell system according to claim8 wherein said third volume of material includes shift catalyst.
 10. Thereaction apparatus according to claim 8 or 9 wherein said conduit meanspasses through said third volume of material and includes inlet meanslocated near the downstream end of said third volume of material. 11.The fuel cell system according to claim 8 or 9 wherein said conduitmeans is disposed entirely upstream of said first region of reformcatalyst material.
 12. The fuel cell system according to claim 8 whereinsaid electrolyte is phosphoric acid.
 13. The fuel cell system accordingto claim 8 or 12 wherein said means for directing an oxygen containinggas into said conduit means includes means for directing the exhaustfrom said oxygen electrode into said conduit means, said system alsoincluding means for directing at least a portion of the combustionproducts from said combustion products outlet means of the vessel beingregenerated into said first volume of material at the upstream end ofthe vessel producing the hydrogen containing gas.
 14. The fuel cellsystem according to claim 8 wherein said electrolyte is an alkali metalwhich is molten at fuel cell operating temperatures, said systemincluding means for directing a first portion of the combustion productsfrom the combustion products outlet means of the vessel beingregenerated into the first volume of material in the vessel producinghydrogen, and for directing air and a second portion of the combustionproducts to said oxygen electrode of said fuel cell.